Aerial propeller with variable pitch



Dec. 5, 1939.

C. R. WASEIGE AERIAL PROPELLER WITH VARIABLE PITCH Filed April 25, 1935 .5 Sheets-Sheet 1 NVE N TOR (Jar/es A? mo ydr WaJe/ e Dec. 5, 1939.

. R. WASEIGE AERIAL PROPELLER WITH VARIABLE PITCH Filed A ril 25, 1935 5 Sheets-Shet 2 ATTORNEY-5 Dec. 5, 1939. c. R. WASEIGE AERIAL PROPELLER WITH VARIABLE PITCH Filed April 25, 1935 5 Sheets-Sheet 4 1 1 7/- l I M Q 0 I 1 A V/// 1 4 b y W VIII/l 7/474 yl/II I lull-w.

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Dec. 5, 1939.

c. R. WASEIGE AERIAL PROPELLER WITH VARIABLE PITCH 5 Sheets-Sheet 5 Filed April 25, 1935 Patented Dec. 5, 1939 UNITED STATES PATENT OFFICE 2,181,985 KERIAL PROPELLER WITH VARIABLE PITCH Charles Raymond Waseige, Bueil, France I Application April 25, 1935, Serial No. 18,139

In France '4 Claims.

My invention relates to airscrew propellers with variable and reversible pitch used on aircrafts and has for itsmain object to provide a pitch varying and reversing gear by which it will be possible .to obtain, when in flight for instance,

a very slow variation of the pitch, and, particularly when landing, a vary rapid pitch reversal, in a time which may be about one second.

A second important object of my invention is to provide a pitch varying and reversing gear whereby the pitch will be reversed rapidly from a fixed predetermined negative value to a fixed predetermined positive value and vice versa, without requiring any watch from the aircraft pilot once. the reversal set in, with the consequence that the only way of varying at will the intensity of the braking effect exercised by the reversed propeller on the aircraft will be to vary the propeller speed.

A third object of my invention is to provide connections between the pitch varying and reversing gear, its control means, the propeller driving engine and the control means of the latter, in order to'make some of them dependent on the other or others in some predetermined occurrences with a view to reduce as much as possible the attention required from and the operations to be made by the pilot.

These and other objects and advantagesof my invention will appear thereafter from the description given below by way of example of two embodiments of my invention and this description should be read with the understanding that the form, construction and arrangement of the several parts may be varied within the limits of the claims hereto appended, without departing from the spirit of the invention as expressed in said claims. that while my invention will be fully described in detail with reference only to one particular type of propeller where the driving power required for this variation and reversal is furnished by the propeller driving engine, it is also applicable to aerial propellers with variable and ing power is furnished by the pilot or by an auxiliary motor, electric or other.

In the annexed drawings:

Fig. l is a diagrammatic view, showing a propeller with variable pitch, in which the mechanisms for slow variation and for pitch reversal comprise a common source of power and a speedchanging device,

Fig. 2 is a diagrammatic view of a propeller with variable pitch which employs, as a source It is for instance to be understoodreversible pitch of any other type where the driv-' May 1, 1934 of power for the variation of the pitch, the propeller driving engine itself.

Fig. 3 is a partial diagrammatic view of a form of the controls which can be employed, chiefly in the case of the propeller'shown in Fig. 2, as well as the connections between the controls.

Figs. 4a and 4b are similar to Fig. 3 .but show other parts of the controls and their connections.

Fig. 5 relates to a device for the automatic control of the mechanism for the slow variation of the speed.

Fig. 6 represents a partial modification of the controls shown in Fig. 3.

Fig. 7 shows the dial of the pitch indicator.

Fig, 8 is a diagrammatic view of the general arrangements of the controls for the pitch varying mechanism and the pitch reversing mechanism.

In the embodiment shown in Fig. 1, the source of power for the variation of the pitch is an electric motor I which is supported in such way as to participate in the rotation of the propeller, and it is thus supplied by means of conductin rings 2 which are coaxial with the propeller and work against fixed brushes 3, or inversely.

The said motor is connected with the propeller blades 4 by driving gear comprising a speedchanging device 5, which in this case is a speedchanging device having two ratios, of the type containing a secondary shaft and adapted for direct coupling, but the device might be of any type. The remainder of the driving gear hereinconsists/of a spur gear wheel Gengaging a gear wheel I coaxial with the propeller and formed in one with a set of conical teeth 8 engaging conical teeth 9 mounted on the blade roots I.

The control of the speed-changing device 5 is effected by means of rod-and-link gear of any kind, or like device, comprising a member which is coaxial with the propeller and rotatable with the latter, but which is movable lengthwise, and herein, this consists of a grooved ring ll co-operating with a member which is held against rotation but is movable lengthwise, in this case, a fork l2.

The operating of the fork l2 will permit the use of either of the two ratios of transmission of the speed-changing device 5, thus affording a rapid change of pitch, which is preferably used' for reversing the pitch, or on the contrary, for a slow variation of the pitch, and the change of direction for the pitch variation can be obtained for instance byreversing the motor by means of a usual reversing switch under automatic or manual control.

There is thus provided two gearings of different gear ratio adapted for respective operation, each of which is operatively connectable to the propeller blades to turn each of them, to vary the 5 propeller pitch, to increase and to decrease it, so that one gearing provides for slow changes of pitch up and down and the other for rapid reversal of pitch up and down.

The embodiment shown in Figs. 2, 4a and 4b is another particular embodiment, according to the present invention, of pitch-varying vmechanism comprising differential gearings adapted to be braked by means of a servo-motor using fluid under pressure, such-as oil.

Herein, there are mounted concentrically with the propeller shaft four drums l5, Ni, ii, l8 which are loose on their bearings, and co-operate with brakes I9, 20, 2|, 22. The'adJacent drums l1, l8 are connected together by a set of gearing having the speed ratio of which has a negative algebraical sign, i. e., a gearing such that the drums l1, l8 will rotate in contrary directions, for instance by means of a planetary,

device 23 whose support is secured to the pro- 25 peller shaft. The drums i6, ll are'connected together by transmission gear comprising a planetary pinion 24 whose support can be coupled to or uncoupled from the propeller shaft,-by means of .any suitable clutch device 25, for instance of I the tooth type; the said planetary pinion 24 is engaged on the one hand with a set of teeth on the drum l6, and on'the other hand with the drum by means of a speed-reducing device which herein consists of a worm portion located 86 on the drum i1 and engaging a worm-wheel 21 keyed to a shaft 28 which is at right angles to the propeller shaft, and carries another worm 29 Fig. 4b engaging a suitable wheel 30 keyed to the shaft of the said planetary pinion 24. The drums |5-|6 are also connected together by a set of gearing the gear ratio of which has a negative algebraic sign, employing herein for this Purp se a pinion 3| engaging external and internal sets of teeth located on the respective drums |5|6,-

said pinion being keyed to a shaft 32 parallel to the propeller shaft and journaled in bearings 32a carried inside the propeller casing 33 by the wall of the latter, and thus shaft 32 will rotate with said casing. The movement of rotation of the pinion 3| on its axis is transmitted to the a i several blades by said shaft 32 and amechanism to be further described.

It will be noted that when none of the drums are braked, the whole of this mechanism will rotate as a unit together with the propeller shaft,

without any internal movement. If one of the drums i5 or I6 is braked, and if the support of I the planetary pinion 24 is not secured, as to rotation, to the propeller shaft, the pinion 3| will rotate on its own axis, in one or the other direction depending upon which one ofthe said drums is braked, whereby increasing or decreasing the pitch. On the other hand, the drums l1 and I8 pinion 36a is concentric to said surface.

pinion 24 and of the devices 21 to 34. Hence,

through the medium of the speed-reducing parts 26 to 29, the planetary pinion 24 will turn on its own axis, in one or the other direction, and this movement imparts to the drum IS a displacement with reference to the drum l5 which 5 results, as in the preceding case, in a rotation of the pinion 4| on its own axis in one or the other direction.

It will be noted that there is thus provided two gearings the speed ratios of which are quite different, for the rotation of the blades; the ratio I corresponding to the braking of the drums l5 and I6 will be used for reversing the pitch of the propeller both up or down according to which drum is braked, and the other ratio, obtained by brak- 15 ing the drums l1 and I8 and by the clutching of the support of the planetary pinion 24, "willbe used for slowly and gradually varying the pitch.

The movement of the pinion 3| itself and the movement of its shaft 32 may be transmitted to the different blades 4 by any suitable means. Herein, this transmission is advantageously obtained by the use of av pinion 34 which is mounted on the end of the shaft 32 and engages a gear-wheel 3'5 coaxial with the propeller shaft, thus actuating an epicycloidal speed-reducing device comprising a planetary pinion 36a rolling on a fixed sun wheel 36 concentric with the propeller shaft, said pinion being rotatably fitted on an extension 35a on the hub of the wheel 35. The outer surface of this extension is a cylindrical surface the axis of which is parallel to but at some distance from the propeller axis and tiiig Sa pinion 36a carries an inner toothing- 3612 also concentric to said surface and which engages a set of teeth 31 coaxial with the propeller shaft and rotating together with a bevel pinion 8' engaging a bevel set 9 provided on each blade root iii. This device is practically irreversible.

Thus the invention includes pitch-varying means comprising two epicyclic toothed wheel trains having speed reducing ratios of opposite algebraical signs, that is,'opposite motion.

The bevel wheel 8' is fioatingly mounted, i. e., it is threaded with some radial play on the propeller shaft, and it is axially abutted against a hemispherical abutment 39.

In order to prevent any self-variation of the pitch due to the effects of jarring, it is known to use means for permanently and equally braking the drums, for instance a friction clutch mounted between the same. Herein, this friction clutch 40 is not mounted directly between the drums, but is located between a gear wheel 4|, loose on a secondary shaft 42 which forms part of the device-controlling the pitch indicator, and a wheel 43 rotating with said shaft, the two wheels 4| 43 being positively rotated by the respective drums i5 and I6, whilst the bearings of the shaft 60 42 are stationary. The device controlling the pitch indicator is of a known type with the use of a differential and will not be further described.

Fig. 3 shows the hand lever 50 for controlling the pitch-reversing mechanism. This lever is connected by a rod 5|, or like connecting member, with a device controlling a servo-motor 52 Figure 411 so ,arranged as to separately throw on the brakes J9 and 20. In this case, the servomotor fFig. 4a) operates by fluid under pressure, and comprises for each brake a cylinder 52 and a fluid distributing valve mechanism preferably -adaptedto sumlb'fluidatfull ratetothecylim dot at all times except when completely cut oil. For this purpose, the two valves 54 and II for 75 admission and exhaust of the fluid are oppositely disposed and between their discs is located the end of a lever 55 mounted on a shaft 56 which carries two other levers .51 and 56 which are urged together by a spring 59. One of these levers, 58, is keyed to the shaft 56, the other lever being loose between two stops secured to the shaft and situatedon the respective sides of the extended part of the lever 58, and thus the lever 51 will turn abruptly in one or the other direction under the action of the spring 59 when it proceeds beyond the said extended part. The two levers 51 are connected together by rod-and-link gear or the like and thus the two valves 53 can be closed simultaneously while the two valves are simultaneously open, but only one of the valves 53 can be opened at a time and the corresponding valve 54 closed at that time. Herein, the rod-and-link gear consists of a twoarm pivoting lever 66; to one arm is pivoted a link 6| having a slot 62 in which is engaged a stud 51a mounted on one of the levers, 51; to the other arm is pivoted a-link 63, pivotally mounted on one arm of the rod 5|, which is bent at right angles; the other arm of the rod which is pivoted to the said reversing lever 50 having a slot 64 in which is slidable a .stud 51b pertaining to the other lever 51. Thus the whole mechanism can have three definite positions, that is, a middle'or neutral position in which both valves 53 are closed, and the two valves 54 open and two end positions in which one of the valves 53 is open whilst the other is closed.

Consequently when the hand-lever is moved either way from its neutral position, this will efiect the abrupt opening of one of the valves 53, according to the direction of the displacement of the hand-lever, thus throwing on the corresponding brake. The automatic stopping of the reversal by the release of the brake is effected, in this apparatus, by means of two earns 65 and 66 corresponding to two predetermined values, positive and negative, of the pitch, said cams being positively operated by the mechanism of the pitch indicator, and one orpthe other cam, according to the position of the hand-lever 50, will act upon the lever 60 in order to bring the lever 5.1 of the valve 53 (now open) into a position of unstable equilibrium, beyond which the spring 59 will effect the instantaneous closing of said valve 53 and the opening of the valve 54, as well as the return of the rod-and-link gear and the reversing lever 50 into the neutral position herein represented, in which both valves 54 are open and the two brakes l9 and 20 are re leased.

Further the reversing, lever- 50 is herein connected with the device for the control of the.

supply of carburated mixture to the propeller driving engine through a rod 61 (Fig. 3) pivoted at one end to the said lever 50, and at the other end to a'pivoting cam 68 which acts upon an elastic joint 69 located between two rods 10--1|, one of which, 10, is connected with the engine throttle 1012 (Fig. 3) and the other, 1i, with the hand-lever 12 for the control of this throttle. The joint 69 is made elastic by an elastic or resilient means arranged to urge and hold the rods 16-1l in a predetermined angular position. The connection between the rod 61 and the pivoted cam however provides for some lost motion in order that the cam will not turn when the hand-lever 50 is moved from its 'reversing lever 50 clutch 25 in order that the displacement of the trary, when the lever 50 is moved into its other position, the cam 68 is turned, and it thus moves the joint 69 when this is located on its path. which takes place for positions of the hand-lever 12 corresponding to a small opening of the engine throttle 10b. The movement of the joint 69 thus effects an increased opening of the engine throttle 10b without any displacement of the throttle control lever 12. When the lever 50 returns to its neutral position, the levers 10-1l return into the position of alignment.

As the mechanism for the slow variation of the propeller pitch is also actuated, in this apparatus, by a servo-motor 15 using fluid under pressure, there is interposed in the conduit supplying the fluid under pressure, a. valve 16 adapted for quick opening and closing, the mecha nism for this purpose being, for instance, of the mally open, said rod being pivoted at the other end to a pivoted lever 19 located in the path of the cam said cam is connected with the throttle control lever 12, and its outline is such that the rod 11 will be maintained, against the action of the spring 18, in aposition in which the valve 16 is closed, whilst the hand-lever 12 is in the position in which the opening of the engine throttle is below a predetermined value.

In order to avoid all improper working, it is necessary that the mechanism for the slow variation of the pitch should not be actuated while the pitch-reversing mechanism is in action. For this purpose, use may be made of a control device similar to the control of the mechanism for slow variation of the pitch, by the throttle control lever 12, and it is preferable to employ such a device, as herein represented. For this purpose, the lever 19 co-operates with a cam 8| mounted on the reversing lever 50, and the, outline of the cam is such that it is only when the lever 50 is in the neutral position that the lever 19 may be brought by the spring 18 into the position corresponding to the opening of the valve 16.

Furthermore, in the construction shown in Fig. 2, it is necessary, in order that the reversing mechanism may operate, that the support of the planetary pinion 24 shall be released. For this purpose, a connection is provided between the and the movable part of the hand-lever 56 from its middle position will effect the release of the said support. Herein, this connection makes use of the said cam 8| and the lever 19 whose angular displacements are transmitted by suitable rod-and-link gear 82, or like device, to a pivoted fork 63 which moves the said movable part lengthwise, by means of a grooved collar 84 coaxial with the propeller shaft. The clutching, which might be effected by the pilot at will, is herein automatically-effected by the action ofan antagonistic spring 85.

A method for the control of the mechanism for the slow variation of the pitch, in such way that this mechanism cannot be actuated when the pitch has a negative value, is shown in Fig. 6, in which the control of the reversing mechanism is employed for this purpose. The cam 8|, which cuts out the mechanism for slow variation during the operating of the reversing mechanism, is herein divided into two parts Ma and Nb; the

part 8la turns together with the hand-lever 50,

tenon 86 will come against-one end of the groove 81, thus moving the part Mb 01 the cam, which then bears upon the lever 19 and actuates the cut- 10 out device I6 to 19, as well as the mechanism 82-85 which controls the clutch 25. When the handle 58 returns to the neutral position, the tenon 86 will slide in the groove 81 without moving the member Bib, which thus continues to 5 hold down the lever I9. The mechanism for the slow variation of the pitch will thus remain out of action as long as the pitch is negative. When the hand-lever 58 is then moved into the position corresponding to the positive pitch, the g9 tenon 86 will meet the other end of the groove 81, thus returning the member 8"; to the initial position, but the part 8Ia of the cam.is now substituted for the part 8"; in order to hold down the lever I9. When the hand-lever 58 25 returns to the neutral position, the tenon 86 moves in" the groove 81 without displacing the I cam piece 8) and the part 8: is withdrawn, thus alowing the lever 19 to rise and hence to release the mechanism for the slow variation 01' 31) the pitch.

Fig. 3 also shows an example of the construction of a device adapted to prevent the racing of the engine when the propeller pitch comes to zero and when the engine throttle is well open.

35 i For this purpose, the present apparatus comprises a rotating cam 88 connected by suitable transmission means 88a with the mechanism 42 controlling the pitch indicator. The said cam actuates a lever 89 pivoting on a stationary axle 40 89a, and also pivoted to the rod-and-link gear I8|8a controlling the engine throttle 18b. It will be noted that the position of the lever 89 thus depends upon the position of the engine throttle 18b, and when the latter is sufliciently closed, the cam 88 can rotate'without meet n the lever 89 when the pitch passes through the zero value. n the contrary, when the throttle 18b is well open, the lever 89 comes upon the path of the cam 88 and the cam will thus act upon the lever at the time when the. pitch passes through the zero point, thus momentarily closing the engine throttle 18b.

Fig. shows a device for the automatic control of the mechanism for the. slow variation of the pitch according to the engine speed. Herein, the centrifugal governor 98 is driven by the engine and it controls the valve-gear of the servomotor I5 by means-of the lever 9|. The tension of the spring 92 can be regulated while running, 60 by the displacement oi. one of its supports consisting of a nut 93 mounted on a threaded rod 96v which can be rotated by suitable driving means, herein comprising thebevel gear wheels 95-96, the latter wheel being driven by the pinion 91 65 engaging a rack 98 actuated by a rotating cam 99 secured to a gear-wheel I88 engaging alike wheel I 8| rotatable by means of a hand-lever I82 together with a pointer I83 moving over a dial I84 graduated in numbers of revolutions.

70 Thus the displacement of the hand-lever I82 regulates the speed of the engine by causing a variation of the pitch, and the governor 98 will then keep this speed automatically constant by suitably actuating the mechanism for the slow 7 variation of the pitch according to the conditions of flight, whether on a level, or for rise or descent, or the like.

Fig. 5 also shows a form of construction of a device for limiting the speed control of the governor to a range comprised between two ex- 5 treme values. Said device herein consists of two stops I85 located on the path of the hand-lever I82,-in such way that this lever cannot assume a position outside of the sector which is thus-defined and which corresponds to engine speeds on 10 either side of the normal working speed'and not tar from the latter. The extreme positions of the hand-lever I82 correspond to the extreme speeds which the engine cannotexceed as long as the automatic mechanism for slow variation of the pitch is enabled to act. On the contrary, when this automatic pitch-varying mechanism is out 01 action due-to the position of the throttle control lever I2, which position determines a reduced admission of carburated mixture, the engine can run at slow speed at difl'erent speeds which depend upon the different positions of throttle lever 12, while stopping the action of the automatic mechanism for the slow variation of the pitch. 23

Fig. 4b shows a form of construction of a hand. control II8 for bringing the propeller blades in line with the direction of the wind,'in the case in which the oil pressure becomes reduced, or in case of other defective action. The said control H8 herein consists of a device of a known type operating by cable and acting directly upon a lever III controlling a brake shoe 22, and when this latter is applied, it will cause a gradual increase of the pitch. The general operation of a the apparatus as a whole is as follows:

Operation When the apparatus is used on board an aircraft, the reversing lever 58 is normally in its 0 middle or neutral position as shown in Fig. 8 and the valve I6 is open so that the mechanism for slowand progressive variation of the pitch is operative whereas the pitch reversing mechanism is kept out of operation. In normal flight, the centrifugal governor 98 actuates this pitch varying mechanism in a known manner by the medium of the rod 9| to constantly keep the engine speed at the value readable on, the dial I84 and determined by the position given to the control lever I82, as explained above with reference to Fig. 5, whatevergis the position given to the control lever I2 and the flight conditions, i. e., whether the aircraft is flying up or down.

However, and as explained herein before, when the control 1everI2 is moved to close the throttle 18b beyond a predetermined limit, the cam 98 comes into engagement with the pivoting lever I9 and constrains the latter to turn against the action of the spring 18, whereby pushing the rod I1 and closing the valve I6. The servo-motor I5 is thus brought out of action and no further variation of the pitch takes place as long as the engine throttle 18b remains substantially closed, so that the engine can nm at any desired slow 85 speed.-

When the pilot wishes to brake the aircraft, for instance on landing, he moves to the left oi Fig. 8 the control lever 58 of the pitch reversing mechanism, whatever is the position of the engine control lever 12. As herein before described with reference to Fig. 3, the pitch is rapidly reversed and broughtto a predetermined negative value in a time of about one second; the braking action of the propeller is then controlled by the pilot latter against the spring 18, whereby pushing the rod 1! and closing the valve 16 so that the servo-motor l5 and consequently the pitch varying mechanism are out of action. As soon as the control lever is automatically return to its middle position upon completion of the reversal, the spring 18 rotates back the lever F9 to its prior position and draws along the rod ll, thereby opening the valve 16 and putting again in operation the pitch varying mechanism.

To again give to the propeller a propelling action instead of a braking action, the pilot moves the control or reversing lever Ell to the right of Fig. 3 and the pitch reversing mechanism operates to bring the pitch to a predetermined positive value while the pitch varying mechanism is again kept out of action until the lever to has been automatically returned to its middle position.

During each reversal operation, the mechanism 88 to 89a,-Fig. 3, operates in a known manner'to momentarily close the throttle ilib when the pitch is passing through the zero value.

In the case of the mechanism shown in Fig. 6, the pitch varying mechanism is not automatically set into operation by the return of the reversing lever 50 to its middle position after the pitch reversing mechanism has brought the pitch to the predetermined negative value but remains out of operationas long as the pitch has this negative value. The pilot must first move the reversing lever 50 to the right in order that the reversing mechanism brings the pitch" from said negative value to the predetermined positive value and-unlocks the pitch varying gear by the return of the reversing lever from its right hand position to its middle position.

Fig. '7 shows a particular type of dial for pitchindicator adapted for a propeller having the principal features of the invention. The said dial has four very apparent indicating marks corresponding to the four principal values or the pitch, 1. e., an infinite value of the pitch, a predetermined negative value, a zero value, and a positive predetermined value, preferably the value which is suitable for the starting of the aeroplane from the ground.

Obviously, the invention is not limited to the details of construction herein described and represented, which are given solely by way of example. Y

What I claim is:

1. An air-screw propeller with variable and reversible pitch comprising in combination a propeller hub, a plurality of blades having each a root so journaled on said hub as to berotatable to an extent from a positive pitch value to a negative one and vice versa, a pitch varying mechanism and a pitch reversing mechanism adapted for selective operation, each of which mechanisms includes a gearing and the gearing of the pitch reversing mechanism has a much smaller gear ratio than the gearing. oi the pitch varying mechanism, each of said mechanisms being capable of turning said blades to vary the pitch both positively and negatively, the reversing mechanism further including a movable control member adapted to control the operation of the reversing mechanism and to be given always thesame position when the mechanism operates to reverse the pitch from a positive value to a negative one, a movable member connected to said blades to have a variable position depending upon the actual pitch value and arranged to actuate said control member to stop the reversing mechanism when reaching a position corresponding to a predetermined negative value of the pitch.

2. An air-screw propeller as in claim 1, wherein said pitch varying mechanism and pitch reversing mechanism include a change-speed gear.

3. An air-screw propeller with variable and reversible pitch comprising in combination a propeller hub, a plurality'of blades having each a root so journaled on said hub as to be rotatable from a position of positive pitch value to a negative one and vice versa, a pitch varying mechanism connected to said blades to be capable of slowly turning each of them in contrary directions, a pitch reversing mechanism conoperative only as long as said pitch reversing mechanism is in operation.

4. An air-screw propeller with variable and reversible pitch comprising in combination a propeller hub, a plurality of blades having each a root s0 journaled on said hub as to be rotatable from a position of positive pitch value to a negative one and vice versa, a pitch varying mechanism connected to, said blades to be capable of slowly'turning each of them in contrary directions, a pitch reversing mechanism connected to said blades to be capable of turning each of them in contrary directions at a much faster rate than. the pitch varying mechanism, a governor responsive tothe engine speed and connected to the pitch varying mechanism to automatically control the latter and a connection between the pitch varying mechanism and the pitch reversing mechanism, said connection being so constructed and arranged that the pitch varying mechanism is dependent on the pitch reversing gear in such a way as to be inoperative as long as the pitch has a negative value.

CHARLES RAYMOND WASEIGE. 

